On-line analysis of ethanol electrochemical oxidation process in a lowtemperature direct ethanol fuel cell

Hereby we present a novel experimental set-up for on-line detection of volatile products formed in a low-temperature fuel cell. The developed set-up, consisting of mass spectrometer and NDIR CO2-sensor, was applied to analysis of anode product distribution of a DEFC equipped with model ethanol electrooxidation catalysts (Pt/C and PtRu/C). The methodology used by us allowed for an on-line detection of electrochemical products of ethanol oxidation with exclusion of products of ethanol oxidation occurring without electron flow in the external circuit (as a result of currentless oxidation by oxygen permeating from the cathode). For instance, it allowed us to observe a distinct time-dependency of CO2 amounts (as well as for current density) in constant voltage experiments for high- and low cell voltage when Pt/C anode catalyst was used, which was not observed for PtRu/C. We proposed a probable explanation based on dependency of ethanol permeation rate on cell parameters. Gas chromatography was used as a supplementary technique for acetic acid detection (a non-volatile product of ethanol oxidation) and allowed us, in connection with MS and CO2-sensor results, to assess the selectivity of the catalysts used at different cell conditions (voltage, temperature etc.). In order to better understand the oxygen crossover phenomenon and its possible effect on the determined amounts of all three main products of ethanol oxidation (acetaldehyde, acetic acid and CO2), a correction for amounts formed at the open circuit voltage was performed. As the CO2 was observed in the anode stream in currentless condition, we assumed that it originates from chemical oxidation of ethanol and/or CO adsorbed on the surface of the anode catalyst, by oxygen permeating from cathode. Based on our results, and the literature data for H2/O2 fuel cell fed with H2/CO mixture, to the anode, we concluded that oxygen permeation can be beneficial for a working ethanol fuel cell, as it allows for anode depoisoning.